Downhole tool for pressure testing of oil and gas wells

ABSTRACT

A downhole tool for pressure testing of oil and gas wells comprises a generally tubular main tool (1), which is provided with an internal passage (2) and is arranged for attachment at the lower end of a drill pipe string. The main tool (1) is on its outside provided with an inflatable packing element (10), which may be supplied with and relieved of inflating medium via an annular slide valve (5) arranged inside the main tool (1). The slide valve has two active positions, one on each side of a closing initial position, and the slide valve is brought to the active positions by an auxiliary tool (18) which may be run into the passage (2) of the main tool and attached releasably in the slide valve (5). By pressure on the upper side of the auxiliary tool (18), the slide valve may be moved to one of its active positions against the action of a valve spring (6), and by traction in a cable attached to the auxiliary tool (18) the slide valve (5) may be moved to its other position against the action of the same valve spring (6). Upon completed pressure testing and relieving of the packing element (10), the auxiliary tool (18) may be freed from the slide valve (5) by varying the traction in the cable in order to release and free a locking mechanism (36-39) in the auxiliary tool (18), whereupon the latter may be pulled up to the surface.

The present invention relates to a downhole tool, e.g. for pressuretesting of oil and gas wells, comprising a generally tubular main toolwhich is provided with an internal passage and is arranged to beattached between a drill pipe string and a drill bit or the like, saidmain tool on its outside being provided with an inflatable packingelement which may be supplied with and relieved of inflating medium viaan annular slide valve arranged internally in the main tool, said slidevalve being movable against the action of a valve spring from a closinginitial position to a first position wherein inflating medium may besupplied to the packing element and a second position wherein theinflating medium is permitted to leave the packing element, by means ofat least one auxiliary tool which is lowerable through the drill pipestring at the end of a cable, the slide valve being provided with acentral, through-going passage which has an inwardly extending shoulderagainst which a portion of the auxiliary tool may be brought to sealingabutment and by means of pressure move the slide valve in the directiontowards the drill bit or the like to said first position.

Such a downhole tool is known e.g. from U.S. Pat. No. 3,529,665. Here,the slide valve is divided into two mutually axially movable parts, thelower part having a smaller internal diameter than the upper part. Whenthe packing element is to be inflated, a first auxiliary tool is loweredwhich passes the upper part of the slide valve and comes to sealingabutment against a shoulder on the lower part, whereupon pressurizing ofthe drill string causes the first auxiliary tool to displace the lowerpart of the slide valve downwards against the action of the valvespring, so that a passage to the packing element is opened for inflatingit. Upon completed pressure testing the first auxiliary tool is raisedand replaced by an auxiliary tool having larger diameter, which uponbeing run down comes to rest against a shoulder on the upper part of theslide valve. Upon pressurizing the drill string, both the upper andlower parts of the slide valve are moved downwards against the action ofthe valve spring, thus opening a relieving passage from the packingelement to the outside of the main tool via an annular space in theupper part of the slide valve. This structure is not known to be used inthe oil industry, a possible explanation being that it is toocomplicated to use or that it cannot satisfy the strict reliabilityrequirements imposed in offshore oil drilling. Furthermore, it will bedifficult or impossible to use in deviation drilling or in horizontalwells.

It is therefore common to undertake formation strength testing only atthe shoe of the casing pipe of the well. If, nevertheless, it isnecessary to test an open hole, this is done by pulling the drill stringout of the hole, dismantling the drill bit etc. and attaching aninflatable packing element to the drill string, which is again run downinto the hole to the desired depth. The packing element is subsequentlyinflated in order to close the hole, whereupon pressure testing of thehole below the packing element may be performed. When the test has beenperformed, the packing element is deflated and the drill string ispulled out. The packing element is removed, the drill bit etc. installedand the drill string again run down into the hole to continue thedrilling. This is a very time consuming and expensive process whichtherefore often is omitted, i.a. leading to reduced safety.

Thus, it is an object of the present invention to provide an improvedtool of the above mentioned type which is well suited for horizontalwells and which, nevertheless, has a simple and reliable structure andis easy, safe and quick to use. It is also an object of the invention toprovide a tool which has a wide field of application so that it i.a. maybe used for selective pressure testing above or below the tool in anopen hole, selective pressure testing above or below the tool in casingpipe, pressure testing of hole strength above or below the tool in orderto determine formation strength, rock stresses, pore pressure, materialproperties, well fluid properties or other geological and rockmechanical parameters, initiation of fissures for later geophysicalinterpretation, and formation strength testing in the contact area ofthe packing element.

This is obtained according to the invention with a downhole tool of thetype mentioned in the introduction, which is characterized in that theauxiliary tool is provided with means for releasable attachment in theslide valve and that the slide valve may be brought to said secondposition by means of tension in the cable and there will be located onthe opposite side of its initial position with respect to its firstposition. This permits using one and the same auxiliary tool both forinflating and deflating the packing element and without having to removethe auxiliary tool during the testing.

An advantageous embodiment of the invention is characterized in that theauxiliary tool comprises a central rod which at its lower end isprovided with an enlarged head for introduction into the central passageof the slide valve to said sealing abutment against said shoulder, andthat a locking device is arranged axially movable under the action ofspring force on the central rod and is provided with members which, whenmoved axially with respect to the head, cooperate with the head in orderto fix or release, respectively, the head in the slide valve, said axialmovements being obtainable on the one hand by means of pressureactivation and on the other hand by means of varying tension in saidcable. This provides for a simple operation which easily may beconducted in a safe manner.

For better understanding of the invention it will be described moreclosely with reference to the exemplifying embodiment shown in theappended drawings, where:

FIG. 1 shows a longitudinal section through a main tool for a downholetool according to the invention;

FIG. 2 shows a longitudinal section through an auxiliary tool for usetogether with the main tool in FIG. 1; and

FIGS. 3-10 are longitudinal sections showing the auxiliary tool in FIG.2 located in the main tool of FIG. 1 and illustrate various steps of theuse of the downhole tool according to the invention.

Both in this description and in the following claims the expressions"upper" and "lower" relate to a vertical application position of thedownhole tool. This is not meant to constitute a restriction since thetool may function in any orientation.

First it is referred to FIG. 1, which shows a main tool 1 for a downholetool according to the invention. The main tool is provided with aninternal passage 2 and is at its upper end provided with internalconical threads 3 for screwing in the lower pin of a drill string (notshown). The drill string will have a somewhat larger internal diameterthan the internal passage 2 of the main tool. The internal passage hasan enlarged portion 4 wherein a slide valve 5 is slidably arranged andis held in a middle initial position by means of a valve spring 6. Thespring acts between two support rings, which abut against both aninwardly extending collar in the main tool and an outwardly extendingcollar on the slide valve. The valve spring 6 is biased, e.g. with aforce of 1750N for a tool having an external diameter of 7" (178 mm).

On its outer periphery the slide valve 5 has two axially spacedcircumferential grooves, which through an internal passage each in theslide valve communicate with the internal passage 2 of the main tool. Inone of the passages a non-return valve 8 is arranged to limit fluid flowto the direction from the internal passage of the main tool. Bydisplacing the slide valve 5 to its upper or lower end positions, one orthe other of the circumferential grooves will be brought in fluidcommunication with a connecting passage 9 leading to an inflatablepacking element 10 arranged on the outside of the main tool 1 on a lowerpart of the latter having reduced diameter. In the deflated conditionthe packing element 10 is maintained in stretched condition by means ofa spring 11 acting on a slidable end sleeve 12, so that the packingelement 10 in inactive position has a somewhat smaller outer diameterthan the largest diameter of the main tool 1. It will be seen that whenthe slide valve 5 moves to its lower position, a connection isestablished between the internal passage of the main tool and theconnecting passage 9 for inflating the packing element since thenon-return valve 8 only permits flow in the direction towards thepacking element, while when the slide valve is located in its upperposition, there is a free passage between the packing element and theinternal passage 2 for deflating the packing element.

The slide valve 5 is provided with a central through-going passage 13,which at its lower end has an inwardly extending shoulder 14, thefunction of which will be explained in connection with FIGS. 3-10.Besides, it will be seen that when the slide valve 5 moves downwards orupwards from its initial position, in both cases the valve spring 6 willbe compressed because one of the support rings 7 will remain stationaryagainst the collar on the main tool while the other is moved by theslide valve.

At the upper end of the internal passage 2 the main tool 1 has ashoulder 15 and somewhat lower a slightly enlarged portion 16, thefunction of which also will be explained in connection with FIGS. 3-10.At its lower end the main tool has a lower sub 17, which e.g. may beconnected to a drill bit or the like.

It is next referred to FIG. 2, where an auxiliary tool 18 for thedownhole tool according to the invention is shown. The auxiliary toolhas a central rod 19, 20 consisting of an upper part 19 and a lower part20. The lower part is provided with an enlarged head 21 at its lowerend, while the upper part 19 slidably receives a pumping down element 22provided with several flexible seals 23 for sealing against the insideof the drill string during pumping down of the auxiliary tool. Thepumping down element is fixed on the rod 19 by means of a shear pin 24,and on a portion above the shear pin the rod is provided withlongitudinal recesses 25 which will form passages for drilling mud andwell fluids past the pumping down element 22 when the latter isdisplaced a distance upwards along the rod as compared to the positionshown in FIG. 2. Furthermore, the rod 19 has a portion 26 which,contrary to the rest of FIG. 1, is shown in radial section and ispresented at a larger scale in a separate picture, contains two radiallymovable stopper pins 27, which biased by a spring 28 will be movedoutwards when they are freed as the pumping down element 22 movesupwards along the rod 19. After they are freed these stopper pins 27will prevent the pumping down element 22 from moving back down along therod 19 far enough for the lower end of the longitudinal recesses 25 tobe covered so that this flow passage is closed, as otherwise mighthappen during pulling up of the auxiliary tool. At its upper end the rod19 is provided with an attachment 29 for e.g. a common tool runningcable (not shown).

The lower part 20 of the central rod is at its upper end provided with aflexible seal 30 which acts as a piston for driving the auxiliary toolinto the main tool after the shear pin 24 of the pumping down element 22has been broken. The seal 30 rests against the upper end of a springhousing 31, which encloses the central rod 20 and is provided with ashear pin 32 fixing the spring housing against axial displacement on therod. The spring housing 31 defines an annular space containing a mainspring 33 and an oppositely acting secondary spring 34. These are withtheir one end resting against an interposed collar 35 having limitedaxial displaceability, while the opposite end of the secondary spring 34acts on a portion 36 of a locking device 37 which is held with limitedaxial displaceability in the spring housing 31. The locking device 37has arms 38 extending out from the spring housing 31 down to the head 21on the lower part 20 of the central rod, the arms 38 being provided attheir free end with a radial enlargement 39. At its opposite end thespring housing 31 is provided with a cavity 40, into which the seal 30may be pulled under deformation and be made inactive as a piston whenthe spring housing moves under the influence of the main spring 33 alongthe rod 20 following shearing of the shear pin 32. This avoids thepacking 30 forming a brake during the pulling up of the auxiliary tool.

It will be seen that the auxiliary tool may be divided at the transitionbetween the upper part 19 and the lower part 20 of the central rod. Theupper part is used when the auxiliary tool is to be pumped down to themain tool, e.g. for deviating or horizontal wells, while if the well isapproximately vertical, the lower part may be replaced by a suitableweight (not shown).

The operation of the tool according to the invention shall now bedescribed with reference to FIGS. 3-10. It is pointed out that the drillstring to which the tool is attached, is deleted in these drawings,which causes the pumping down element of the auxiliary tool to be shownin its undeformed condition, while its flexible seals 23 actually wouldlie bent upwards in the central cavity of the drill string. Besides, thecable that has to be attached to the upper end of the auxiliary tool isnot shown, and in order to save space, the lower part of the main toolwith the inflatable packing element is not shown either. As regards thereference numerals to be used in the following description, it isreferred to FIGS. 1 and 2.

In FIG. 3 the auxiliary tool 18 has been run as far down into the maintool I that the lower end of the pumping down element 22 has come torest against the upper shoulder 15 of the main tool 1. Here, theauxiliary tool is in the same condition as in FIG. 2, and for a tool ofthe dimension mentioned in connection with FIG. 1 above, the biasingforce of the main spring 33 and the secondary spring 34 may e.g. be1581N and 374N, respectively. The radial enlargements 39 on the lockingarms 38 rest against a portion of the head 21 having an intermediatediameter.

In FIG. 4 the auxiliary tool has been moved a further distance into themain tool by means of pumping and/or the momentum of the auxiliary tool.The shear pin 24 has been sheared and the pumping down element 22 hasbeen left hanging on the shoulder in the main tool. The head 21 of thecentral rod of the auxiliary tool has penetrated partly into the centralpassage 13 in the slide valve 5, and the radial enlargements 39 on thelocking arms have come to abutment against the upper end of the slidevalve.

FIG. 5 shows the situation after further pumping has taken place. Thehead 21 of the auxiliary tool has penetrated even further into thepassage in the slide valve, the locking device 36-39 having been pushedsomewhat upwards against the action of the secondary spring 34, theforce of which now has increased to 561N. The free ends of the lockingarms 38 have thus come to rest against a narrower portion of the head21, their enlargements 39 having been pushed sufficiently inwards to beable to pass the upper edge of the slide valve and into its centralpassage.

In FIG. 6, further pumping has brought the head 21 to sealing abutmentagainst the inwardly extending shoulder 14 in the slide valve, and theenlargements 39 have passed the narrowest portion of the central passageof the slide valve so that they have resumed their initial position andthe secondary spring has gone back to its resting position. Furthermore,the pumping has led to the slide valve having been moved to its lowerposition, and the circumferential groove on the slide valve connected tothe non-return valve 8 has been brought in contact with the connectingpassage 9 leading to the inflatable packing element. The pressure in theinternal passage 2 of the main tool is thus transmitted to the packingelement for inflating same. The magnitude of the inflating pressure isregulated by a drilling mud/cement pump on the surface. With the slidevalve in its lower position the force of the valve spring 6 is increasedfrom 1750N to 2600N.

In all four steps shown in FIGS. 3-6 there has been no pull in the cableconnected to the upper end of the auxiliary tool.

When sufficient pressure has been obtained in the inflatable packingelement so that it seals as desired against the bore hole wall, a pullof about 1000N is exerted in the cable. This leads to the situationshown in FIG. 7. Here, the head 21 of the auxiliary tool has been movedaway from its seat against the shoulder 14 in the slide valve, but thehead is still held in the central passage of the slide valve since thelocking enlargements 39 have come to abutment against the lower edge ofthe upper, narrower passage of the slide valve. The slide valve has beenmoved back to its middle initial position by the valve spring 6 and willremain in this position notwithstanding the action of the cable tensionbecause the latter is only about 1000N while the biasing force of thevalve spring is 1750N. With the auxiliary tool in this position, therewill be free passage for drilling mud down to the bottom of the well,e.g. due to the position of the seal 30 in the somewhat enlarged portion16 of the internal passage 2 of the main tool. In this situationpressure testing of the formation, for example, may be performed.

Upon completed testing the traction in the cable is increased to about3000N. This pulls the slide valve to the upper position by means of thelocking enlargements 39. This position of the slide valve is shown inFIG. 8 and provides passage for the inflating fluid in the packingelement to the internal cavity of the main tool so that the packingelement 10 is brought to resume its initial position by means of thespring 11. With the slide valve still in the upper position, the cabletraction is increased to about 5000N, so that the shear pin 32 holdingthe spring housing 31 to the lower part 20 of the central rod of theauxiliary tool, is sheared, whereby the situation shown in FIG. 8occurs. Under these circumstances the force in the main spring 33 willbe 2356N and in the secondary spring 140N. In the next step, which isillustrated in FIG. 9, the pull in the cable is slackened. The mainspring 33, which now is free at its upper end, pushes the central rod ofthe auxiliary tool downwards until the upper end of the spring housingcomes to rest against the seal 30, which at the same time is pulled intothe cavity 40 of the spring housing. Concurrently the enlargements 39 ofthe locking arms 38 move free of the enlarged head 21 so that it will nolonger be locked in the slide valve which, moreover, has moved back toits initial position.

In the last step, which is illustrated in FIG. 10, the auxiliary tool ispulled out of the main tool and further up to the surface, where theauxiliary tool may be readied for further use by inserting new shearpins 24 and 32. From FIG. 10 it may be seen that during the pulling up,the lower end of the pumping down element 22 has come to rest againstthe extending stopper pins 27, thus making an open passage inside thepumping down element through the longitudinal recesses 25 in the upperrod 19. Since the seal 30 has been pulled into the cavity 40 of thespring housing, it will not present any resistance against the pullingup either.

In case malfunctioning or blocking of the valve system should occurduring use of the tool, or the cable should be pulled apart while thepacking element is inflated, a hollow shear pin 41 (FIG. 1) has beenincluded in the upper end of the packing element as a safety precautionin order to facilitate emptying of the packing element. The packingelement may be emptied through the hollow shear pin upon its shearing byrotation of the drill string.

It will be understood that the invention is not limited to theexemplifying embodiment described, but may be varied and modified in anumber of ways within the inventive idea and the scope of the followingclaims.

We claim:
 1. A downhole tool comprising a generally tubular main tool(1) which is provided with an internal passage (2) and is arranged to beattached between a drill pipe string and a drill bit, said main tool (1)on its outside being provided with an inflatable packing element (10)which may be supplied with and relieved of inflating medium via anannular slide valve (5) arranged internally in the main tool (1), saidslide valve (5) being movable against the action of a valve spring (6)from a closing initial position to a first position wherein inflatingmedium may be supplied to the packing element (10) and a second positionwherein the inflating medium is permitted to leave the packing element,by means of at least one auxiliary tool (18) which is lowerable throughthe drill pipe string at the end of a cable, the slide valve (5) beingprovided with a central, through-going passage (13) which has aninwardly extending shoulder (14) against which a portion (21) of theauxiliary tool (18) may be brought to sealing abutment and by means ofpressure move the slide valve (5) in the direction towards the drill bitto said first position, characterized in that the auxiliary tool (18) isprovided with means (31-39) for releasable attachment in the slide valve(5) and that the slide valve (5) may be brought to said second positionby means of tension in the cable and there will be located on theopposite side of its initial position with respect to its firstposition.
 2. A downhole tool according to claim 1, characterized in thatthe auxiliary tool (18) comprises a central rod (19, 20) which at itslower end is provided with an enlarged head (21) for introduction intothe central passage (13) of the slide valve (5) to said sealing abutmentagainst said shoulder (14), and that a locking device (36-39) isarranged axially movable under the action of spring force on the centralrod (19, 20) and is provided with members (39) which, when moved axiallywith respect to the head (21), cooperate with the head in order to fixor release, respectively, the head in the slide valve (5), said axialmovements being obtainable on the one hand by means of pressureactivation and on the other hand by means of varying tension in saidcable.
 3. A downhole tool according to claim 2, characterized in that alower part (20) of the central rod (19, 20) the auxiliary tool (18) isenclosed by a spring housing (31) which is provided with a shear member(32) fixing the spring housing against axial displacement on the lowerpart (20), said spring housing (31) defining an annular space containinga main spring, (33) and an oppositely acting secondary spring (34), saidsprings being supported at their one end against an interposed collar(35) with limited axial mobility, the opposite end of the secondaryspring (34) biasing the locking device (36-39), which has a portion (36)which is held captive with limited axial mobility in the spring housing(31).
 4. A downhole tool according to claim 3, characterized in that thelower part (20) of the central rod (19, 20) of the auxiliary tool (18)is provided with a flexible seal (30) acting as a piston for driving theauxiliary tool into the main tool (1).
 5. A downhole tool according toclaim 4, characterized in that the spring housing (31) at its upper endis provided with a cavity (40) for receiving said seal (30) acting as apiston in order to make the piston inactive when the spring housing (31)is moved under the influence of the main spring (33) after the shearmember (32) of the spring housing having been sheared.
 6. A downholetool according to one of claims 2-5, characterized in that the auxiliarytool (18) is provided with a pumping down element (22) which is attachedto an upper part (19) of the central rod (19, 20) of the auxiliary toolby means of a shear member (24).
 7. A downhole tool according to claim6, characterized in that the Upper part (19) of the central rod, on aportion above the shear member (24), is provided with longitudinalrecesses (25) forming passages for drilling mud and well fluids uponrelative displacement of the pumping down element (22) upwards along thecentral rod (19, 20).
 8. A downhole tool according to claim 7,characterized in that the portion of the upper part (19) of the centralrod (19, 20) having longitudinal recesses (25) is provided with radiallymovable stopper elements (27) which, under the influence of a spring(28), will be moved outwards when they are freed by the upwards movementof the pumping down element (22) along the central rod (19, 20), therebylimiting the movement of the pumping down element along the central rod(19, 20) in the opposite direction during pulling up of the auxiliarytool (18).
 9. A downhole tool according to claim 1, characterized inthat the valve spring (6) is arranged to move the slide valve (5)towards its initial position both from its first and its secondpositions.
 10. A method for pressurizing and relieving an inflatablepacking element (10) on a downhole tool for pressure testing of an oilor gas well, said downhole tool comprising a main tool (1) carried by adrill string at its lower end and comprising the packing element (10) onits outside, wherein the packing element is supplied with and relievedof inflating medium via a slide valve (5) displaceably arranged in themain tool, said slide valve being mowed from a closing initial positionto a first position wherein inflating medium may be supplied to thepacking element (10) and a second position wherein inflating medium ispermitted to leave the packing element, by means of at least oneauxiliary tool (18) which is run down through the drill string at theend of a cable, said auxiliary tool being brought to sealing abutmentagainst an inwardly extending shoulder (14) in a central, through-goingpassage (13) in the slide valve so that the slide valve may be moved atleast to said first position by means of pressure on the upper side ofthe auxiliary tool (18), characterized in that the auxiliary tool (18)is releasably attached in the slide valve (5) and that the slide valveis brought to said second position by means of traction in the cable andis thereby moved to the opposite side of its initial position ascompared to its first position.